Chemistry
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Chemistry - Marcador
Chemistry - Detalles
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| State how the particles of a solid, liquid and gas are arranged. | Solid- Particles are in a fixed pattern(lattice) due to strong forces of attraction so they cannot leave their positions but are able to vibrate. Liquid- Particles can move about and slide past each other, the particles are clos to each other but not in a lattice as the forces holding them are weaker than in a solid. Gas- Particles are far apart and move about very quickly since there's almost no force holding them together. |
| What are the two ways to increase gas pressure? | Decreasing the volume of container increasing the temperature |
| What are the two factors that affect the rate of diffusion | Mass of particles Temperature |
| Definition of diffusion | It is the net movement of particles from a region of higher concentration to a region of lower concentration as result of their random movement. |
| What is meant by saturated solution? | When the solution cannot dissolve no more solute at the temperature. |
| What is an aqueous solution? | A solution of water. |
| What is volatile liquid and what's the reason it is volatile? | A volatile liquid is a liquid that can evaporate easily as a result of its weak bonds(weak forces of attraction). |
| How can you identify an impure substance? | Melting point falls and boiling point rises It melts and boils over a range of temperatures and not sharply |
| The more the impurity there is... | The bigger the change in in melting and boiling points The wider the temperature range over which melting and boiling occurs. |
| Filtration is used to separate ... | A solid from a liquid |
| Crystallisation is used to separate... | A solute from its solution |
| Evaporation is used to separate... | A solute from its solution |
| Simple distillation is used to separate ... | A solvent from its solution |
| Simple distillation is used to separate ... | A solvent from its solution |
| Fractional distillation is used to sperate ... | Liquids from each other |
| Chromatography is used to separate... | Different substances from a solution |
| When filtering the trapped solid is called the... and the liquid passed through is called the... | Residue Filtrate |
| Why does cooling cause crystals to form when using crystallisation? | Since soluble solids are less soluble when temperature is lower, crystals form when temperature is reduced. |
| Give the four steps in the process of crystallisation done in order to separate copper(II) sulfate from water. | 1) The solution is heated to evaporate some of the water to make the solution more concentrated. 2)Eventually the solution becomes saturated, if you cool it now crystals will stat to form. 3) Leave the solution to cool. Crystals start to form in it as the temperature falls. 4) Remove the crystals by filtering, then rinse them with distilled water and dry them with filter paper. |
| What can be done to separate a mixture of salt and sugar? | Water cannot be used since both dissolve in water but Ethanol can dissolve only sugar, so it can be used.( When heating ethanol solution a water bath should be used since ethanol is flammable ). |
| Give the steps to purify water which contains impurities | 1) Heat the solution in the flask. As it boils, water vapour rises into the condenser, leave impurities(salts) behind. 2) The condenser is cold, so the vapor condenses to water in it. 3) The water drips into the beaker. It s called distilled water(it is almost pure) |
| Give the steps to separate a mixture of water and ethanol. | 1) Heat the mixture in a flask. At 78 C the ethanol begins to boil, some water evaporates too. So a mixture of ethanol and water rises up the column. 2) The vapour condenses on the glass beads in the column making the beads hot. 3)When the beads reach about 78 C ethanol vapour can no longer condense on them, only the water vapour does. So the water drips into the flask, the ethanol goes into the condenser where it condenses and pure ethanol drips into the beaker. 4)Eventually, the thermometer reading rises above 78 C, a sign that all the ethanol has gone. |
| Name two places where fractional distillation is industrially used. | Refining crude oil Separate the gases in air. |
| How does solubility of a substance affect of how far it will travel in the chromatography paper? | More the soluble a substance is in a solvent the further it will travel up the chromatography paper. |
| What is locating agent used for? | Used to show up the colorless substances in chromatography, by reacting with them to form colored substances |
| How do you calculate the Rf value? | Distance moved by solute divided by the distance travelled by the solvent. |
| What is an isotope? | Atoms of the same element which have the same proton number but different nucleon number. |
| What is a radioactive isotope? | An isotope with an unstable nucleus. |
| What is a radioactive isotope? | An isotope with an unstable nucleus. |
| Give three uses of radioisotopes | To treat cancer To kill germs and bacteria (sterilization) To check for oil pipe leaks |
| Why are the chemical properties of all isotopes similar. | Since the number of valency electrons are similar their chemical reactions are similar too. |
| Give five physical properties of Non-metals | Brittle(breaks easily) Do not conduct heat or electricity Low boiling and melting points Looks dull in solid state Low density solids |
| Give five physical properties of Metals | Hard and strong Malleable(can be hammered into different shapes) and Ductile (drawn out to make wires) High density High melting and boiling points Good conductors of electricity of heat Looks shiny when polished |
| Give two chemical properties of Non-metals | Form negative ions when they react React with Oxygen to form oxides that are acidic(Their aqueous solutions will turn litmus red) |
| Give two chemical properties of Metals | Form positive ions when they react Reacts with oxygen to form oxides that are bases(the oxides can neutralise acids) |
| Name three signs of a chemical change | One or more new chemical are formed Energy is taken in or given out, during the reaction The change is usually difficult to reserve |
| What are the forces that bonds ionic compounds called? | Electrostatic force |
| Describe the structure of an ionic compound. | They form a giant lattice structure which is a regular pattern containing a very large number of alternating positive ions and negative ions . |
| Give three properties of ionic compounds | Ionic compounds have high melting and boiling points Ionic compounds are usually soluble in water Ionic compounds conduct electricity when melted/dissolved in water |
| Why can ionic compounds conduct electricity when melted/dissolved in water? | When ionic compounds are dissolved in water or melted, their ions become free to move therefore are able to conduct electricity |
| Why do ionic compounds have high melting and boiling point? | Since ionic bonds are very strong lots of heat energy to break up the lattice. |
| Why does magnesium oxide have a higher melting sodium chloride? | This is because magnesium and oxygen ions have double the charges of sodium and chlorine ions. |
| Give three properties of covalent bonds | Covalent compounds have low melting and boiling point and many covalent liquids are volatile. Covalent compounds tend to be insoluble in water Covalent compounds do not conduct electricity |
| Give two examples of macromolecules | Diamond Silicon (IV) Oxide |
| Why are diamonds so strong and have high melting points? | Since each atom is held in place by 4 strong covalent bonds |
| What are allotropes? | Different form of an element. |
| Give two differences between graphite and diamond | Diamonds are hard but graphite is soft and slippery Diamonds can't conduct electricity but graphite can |
| Why is graphite able to conduct electricity? | Since they form only three bonds, the fourth electron is free to move carrying a charge |
| Give three properties and two uses of diamond | Properties -Hardest known substance -Can not conduct electricity -Shiny when cut Uses -Used for cutting -Used for jewellery |
| Give three properties and three uses of graphite | Properties -Soft and slippery -Soft and dark in color -Conducts electricity Uses -Lubricant -Pencil lead -Electrodes |
| Give three properties and three uses of silicon (IV) oxide | Properties -Hard -Lets light through -High melting point Uses -Sandpaper -Glasses and lenses -Bricks for lining surfaces |
| What is a metallic bond? | A bond formed through the attraction between metal ions and electrons |
| Give four properties of metallic bonds and explain the reasons for those properties | Metals USUALLY have high melting points since lots of energy is required to break its strong metallic bonds Metals are malleable and ductile since layers of the metallic bonds can slide past each other without breaking the bond since electrons are free to move too Metals are good conductors of heat as free electrons take in heat energy and quickly transfer throughout the metal structure Metals are good conductors of heat since the free electrons can move through the lattice |
| What is relative atomic mass? | It is the average mass of its naturally- occurring isotopes, relative to the mass of a carbon - 12 atom |
| What is relative molecular mass? | The mass of a molecule found by adding the relative atomic masses of atoms in molecule |
| What is the formula used to calculate percentage purity? | Mass of pure substance divided by total mass multiplied by 100 |
| What is meant by mole of a substance? | It is the amount that contains the same number of units as the number of carbon atoms in 12g of carbon-12 |
| What is the formula to find the mass of a given number of moles? | Mass of given number of moles is equal to mass of 1 mole multiplied by number of moles. |
| What are the conditions of room temperature pressure? | 20 C and 1 atmosphere |
| How do convert from cm cube to dm cube | Divide by 1000 |
| What is the formula used to calculate concentration? | Concentration is equal amounts of solute in moles divided by the volume of solution in dm cube |
| What is empirical formula? | Shows the simplest ratio in which the atoms in a compound are combined |
| What is the formula used to find the %yield? | Actual mass obtained divided by calculated mass multiplied by 100 |
| Give three examples of redox reactions. | Displacement reaction Combustion Metal + Acids |
| What color change is seen when Potassium Iodide reduces another substance? | Colorless to red brown |
| What color change is seen when Potassium Manganate (VII) oxidises another substance? | Purple to colorless |
| Give three ways which can be used to identify if a redox reaction has taken place | Gain and lost of Oxygen Gain and lost of Electrons Changes in oxidation state |
| What is meant by reduction? | A chemical reaction in which a substance loses oxygen or gains electrons/hydrogen. |
| What is meant by oxidation? | The chemical reaction in which a substance gains oxygen or loses electrons/Hydrogen |
| Name three uses of Sodium Hydroxide. | Soaps Detergent Medical drugs |
| How can you electroplate a steel jar using electroplating? | The anode should be made of silver and the steel jar should be the cathode The silver from anode dissolves to form positive ions in silver nitrate solution The silver ions are attracted to the cathode where they form a layer of silver on the steel jar |
| Give two reasons for why electroplating is used | Used to make another metal look better Used to prevent corrosion |
| How can you purify copper using electrolysis? | The anode should be the impure copper and the cathode should be pure copper. The copper in the anode dissolves but the impurity does not they just drop to the floor A layer of the pure copper builds up on the cathode |
| Give two uses of electrolysis excluding decomposition | Refining(purifying) Electroplating |
| Name three uses of Hydrogen | Used to make hydrogen peroxide Used as fuel in hydrogen fuel cells Used to make nylon |
| Name three uses of Chlorine | Used for sterilizing Used to produce hydrochloric acid and hydrogen chloride Used for making plastic PVC |
| What chemicals can be obtained through the electrolysis of brine? | Sodium hydroxide, Chlorine, Hydrogen |
| What is brine ? | A concentrated solution of sodium chloride. |
| In overall what kind reaction is electrolysis? | A redox reaction |
| What kind of reaction takes place in the anode? | Oxidation(since they lose electrons) |
| What is meant by electrolysis ? | Electrolysis is the breakdown of an ionic compound when molten or in aqueous solution using electricity |
| What is an electrolyte? | The liquid which conducts electricity in electrolysis |
| What are electrodes used for? | They are used bring electricity in and out an electrolyte during electrolysis. |
| What are anodes, and what type of ions do they attract ? | The are positive electrodes which attract negative ions(Anions) |
| What are cathodes, and what type of ions do they attract? | They are positive electrodes which attract positive ions(Cations) |
| What is the rule used to decide if a metal or hydrogen forms at cathode when its a solution? | IF the metal is more reactive than hydrogen, hydrogen form at the cathode IF hydrogen is more reactive then metal forms at the cathode. |
| What is the rule used to decide if a another non-metal or oxygen forms at the anode when its a solution? | If it is concentrated solution of halide then halide forms at the anode but if its a dilute solution or no halide then oxygen forms at the anode |
| What kind of reaction takes place in the cathode? | Reduction(sine they gain electrons) |
| Name two elements which could be used to make inert electrodes. | Graphite and platinum |
| What are the optimum conditions for best yield? | High pressure, removal of product from forward reaction Moderate temperature and a catalyst |
| Give one drawback of using hydrogen cells | Hydrogen is very flammable, hence if lighted up can result in an explosion |
| What is a reversible reaction? | A reaction with both a forward reaction as well as a backward reaction, where a product can form then break down. |
| What is meant by equilibrium? | The state where the forward and back reaction is taking place at the same rate in a reversible reaction so there is no overall change. |
| How does changing the temperature affect equilibrium? | If the forward reaction is exothermic increasing the temperature decreases the yield but if it is endothermic increasing the temperature increases the yield |
| How does changing the pressure affect equilibrium? | If there are fewer products than reactants increasing pressure increases the yield |
| How can equilibrium be reached faster? | By raising the temperature and pressure then adding a catalyst |
| Breaking bonds ____ ____ energy and making bonds ____ ____ energy | Take in energy Release energy |
| How can you shift equilibrium when reaction takes place in solution? | By adding more of the reactant ( increasing its concentration) so more product will form By changing temperature ( a rise in temperature will favor endothermic reaction) |
| How does removing the product of forward reaction affect equilibrium? | More product will form in order to restore the balance |